000
AXPZ20 KNHC 120333
TWDEP 

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
0405 UTC SAT DEC 12 2009

TROPICAL WEATHER DISCUSSION FOR THE EASTERN PACIFIC OCEAN FROM 
THE EQUATOR TO 32N...EAST OF 140W. 

BASED ON 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH 
0300 UTC.

...ITCZ...

THE INTERTROPICAL CONVERGENCE ZONE IS ALONG THE LINE...07N78W TO 
08N85W TO 06N100W TO 08N118W TO 06N140W. SCATTERED MODERATE 
CONVECTION IS WITHIN 70 NM N OF AXIS W OF 135W. SIMILAR 
CONVECTION IS NEAR 07N119W.

...DISCUSSION... 

A NEW COLD FRONT HAS ENTERED THE FAR NW PORTION OF THE FORECAST 
REGION WITH SW WINDS OF 20 TO 25 KT IN A SMALL AREA AHEAD OF THE 
FRONT. NLY WINDS LESS THAN 20 KT AND SEAS OF UP TO 9 FT ARE 
EXPECTED IN THE WAKE OF THE FRONT. THIS FRONTAL SYSTEM WILL MOVE 
RATHER QUICKLY ACROSS THE N WATERS AND BECOME DIFFUSE IN ABOUT 
48 HOURS. E OF FRONT...A WEAK RIDGE...ANCHORED ON A 1019 MB HIGH 
LOCATED NEAR 25N121W...COVERS THE AREA N OF 15N W OF 110W. 
ELSEWHERE...A BROAD TROUGH REMAINS CENTERED ALONG THE ITCZ AND 
RUNS FROM 18N126W TO 07N134W. W OF TROUGH...NE WINDS OF 20 TO 25 
KT ARE OBSERVED. A FEW SHIP OBSERVATIONS AND AN ASCAT PASS FROM 
AROUND 1915 UTC CONFIRMED THESE WIND SPEEDS. THE TROUGH IS 
FORECAST TO DISSIPATE IN ABOUT 24 HOURS AND A BELT OF ELY TRADE 
WINDS IN THE 20 TO 25 KT RANGE WILL PERSIST PARTICULARLY FROM 
07N TO 20N W OF 115W. 

DURING THE PAST SEVERAL DAYS...MARINE CONDITIONS W OF 110W ARE 
BEING DOMINATED BY LARGE AND LONG PERIOD NW SWELL AND 
SIGNIFICANT WAVE HEIGHTS. CURRENTLY...THIS SWELL EVENT CONTINUES 
TO PROPAGATE SE BEYOND THE EQUATOR MERGING WITH CROSS EQUATORIAL 
S AND SW SWELLS. THE SEA HEIGHTS ACROSS THE FORECAST REGION ARE 
BEGINNING TO SUBSIDE. A NEW BATCH OF NW SWELL WITH WAVE PERIODS 
BETWEEN 14 TO 15 SECONDS SHOULD REACH THE FAR NW PORTION OF THE 
AREA BY SUN EVENING. THIS SWELL EVENT WILL BE ASSOCIATED WITH A 
STRONG EXTRATROPICAL CYCLONE MOVING WELL N OF AREA ACROSS THE NE 
PACIFIC. 

ALOFT...BROAD UPPER-LEVEL TROUGH WITH AXIS FROM NORTHERN BAJA 
CALIFORNIA SOUTHWEST TO NEAR 20N120W DOMINATES THE NORTH WATERS 
WITH A NEARLY ZONAL FLOW COVERING THE AREA N OF 20N. AN UPPER 
ANTICYCLONE SITUATED OVER THE NW CARIBBEAN EXTENDS A RIDGE OVER 
SE MEXICO AND MOST OF CENTRAL AMERICA INTO THE EPAC PRODUCING 
MODERATE TO STRONG SUBSIDENCE MAINLY E OF 110W. THE EXCEPTION IS 
SOME LOCAL CONVECTION FROM 100W TO 102W ASSOCIATED WITH A WEAK 
SURFACE TROUGH EMBEDDED WITHIN THE ITCZ THAT RUNS FROM 11N102W 
TO 06N104W. AN EARLIER ASCAT PASS SHOWED SOME WIND SHIFT RELATED 
TO THIS TROUGH. 

GAP WINDS...
WINDS HAVE INCREASED TO 20 KT ACROSS THE GULF OF PAPAGAYO AS  
THE PRES GRADIENT BUILDS ACROSS THE WESTERN CARIBBEAN...ALLOWING 
EASTERLY TRADE WINDS TO FUNNEL ACROSS COSTA RICA AND NICARAGUA 
INTO THE EASTERN PACIFIC. WINDS ARE EXPECTED TO INCREASE TO 25 
KT DURING THE OVERNIGHT AND EARLY MORNING HOURS WITH THE AID OF 
DRAINAGE FLOW. 

AN EARLIER WINDSAT PASS SHOWED NLY WINDS OF 20 TO 25 KT ACROSS 
THE GULF OF TEHUANTEPEC. THE NAM REGIONAL MODEL SUGGESTS THAT 
THIS WIND PATTERN WILL PERSIST ACROSS THIS AREA OVER THE NEXT 
COUPLE OF DAYS. 
  
$$
GR